This invention relates generally to joint systems for connecting roofing panels and especially for laminated panels of foam polymeric material. Difficulty has been encountered with joints between roofing panels because of the movement of one panel relative to the next after installation. This can be caused by expansion and contraction of the panels or by seasonal changes in the deck or supporting members on which the panels are mounted. In order to be economically feasible, joint systems for roofing must be relatively simple to install and be durable enough to last for a number of years.